The efficacy of transdermal fentanyl in the treatment of postoperative pain: a double-blind comparison of fentanyl and placebo systems

Forty consenting patients scheduled for abdominal surgery were entered into a double-blind comparison of the efficacy of transdermal fentanyl (TTS-fentanyl) and placebo (TTS-placebo) in the treatment of postoperative pain. All patients were allowed supplementary pethidine (25-50 mg) if pain relief was inadequate provided that their respiratory rate was > 10 breaths/min and there was no pronounced CNS depression. Visual analogue pain scores (VAPS), sedation rating scores (SRS), blood samples for the determination of fentanyl concentration, blood pressure, pulse and respiratory rate were determined hourly for 48 h from the time of TTS system application. The first lot of TTS systems were removed after 24 h and a second lot were applied which remained in situ for a further 24 h. There was no significant difference between the patients in the TTS-fentanyl and TTS-placebo groups in the VAPS throughout the 0-12, 12-24, 24-36 and 36-48 h periods suggesting that the quality of pain relief was similar between the 2 groups. However, significantly less supplementary pethidine was administered to the TTS-fentanyl group in the 12-24, 24-36 and 36-48 h periods. In contrast, the amount of supplementary pethidine administered in the 0-12 h period was similar in both groups which was consistent with the long delay time (mean ± S.D. value of 16.6 ± 10 h) before clinically effective concentrations of fentanyl were obtained from the systems. The profile of side effects was similar in the 2 groups. There were only minor dermatological side effects (erythema and rash) which could be attributed to the formulation and these were not reported as troublesome by any of the patients. The mean measured release rate was similar to the nominal rate although there was considerable variability in the measured release rate at each dose level.